Chemistry II
Final Exam Review Problems
1. Several reactions are carried out using AgBr, a cream-colored salt for which the value of the
solubility product constant, Ksp , is 5.0 × 10−13 at 298 K.
a. Write the expression for the solubility-product constant, Ksp , of AgBr.
b. Calculate the value of [Ag+] in 50.0 mL of a saturated solution of AgBr at 298 K.
c. A 50.0 mL sample of distilled water is added to the solution described in part (b), which is in a
beaker with some solid AgBr at the bottom. The solution is stirred and equilibrium is
reestablished. Some solid AgBr remains in the beaker. Is the value of [Ag+] greater than, less
than, or equal to the value you calculated in part (b) ? Justify your answer.
d. Calculate the minimum volume of distilled water, in liters, necessary to completely dissolve a 5.0
g sample of AgBr(s) at 298 K. (The molar mass of AgBr is 188 g/mol.)
e. A student mixes 10.0 mL of 1.5 × 10−4 M AgNO3 with 2.0 mL of 5.0 × 10−4 M NaBr and stirs the
resulting mixture. What will the student observe? Justify your answer with calculations.
f. The color of another salt of silver, AgI(s), is yellow. A student adds a solution of NaI to a test
tube containing a small amount of solid, cream-colored AgBr. After stirring the contents of the
test tube, the student observes that the solid in the test tube changes color from cream to
yellow.
i. Write the chemical equation for the reaction that occurred in the test tube.
ii. Which salt has the greater value of Ksp : AgBr or AgI? Justify your answer.
ଷା
2. 8 H ା ሺaqሻ + 4 Clି ሺaqሻ + MnOି
ସ ሺaqሻ → 2 Clଶ ሺgሻ + Mn ሺaqሻ + 4 Hଶ Oሺlሻ
Cl2 (g) can be generated in the laboratory by reacting potassium permanganate with an acidified
solution of sodium chloride. The net-ionic equation for the reaction is given above.
a. A 25.00 mL sample of 0.250 M NaCl reacts completely with excess KMnO4(aq). The Cl2 (g)
produced is dried and stored in a sealed container. At 22°C the pressure of the Cl2(g) in the
container is 0.950 atm.
i. Calculate the number of moles of Cl–(aq) present before any reaction occurs.
ii. Calculate the volume, in L, of the Cl2 (g) in the sealed container.
An initial-rate study was performed on the reaction system. Data for the experiment are given in the
table below.
Trial
[Cl2]
[MnOି
[H+]
Rate of Disappearance of
ସ]
MnOି
ସ in M/s
1
0.0104
0.00400
3.00
2.25 × 10-8
2
0.0312
0.00400
3.00
2.03 x 10-7
3
0.0312
0.00200
3.00
1.02 x 10-7
b. Using the information in the table, determine the order of the reaction with respect to each of
the following. Justify your answers.
i. Clି
ii. MnOି
ସ
c. The reaction is known to be third order with respect to H ା . Using this information and your
answers to part (b) above, complete both of the following:
i. Write the rate law for the reaction.
ii. Calculate the value of the rate constant, k, for the reaction.
d. Is it likely that the reaction occurs in a single elementary step? Justify your answer.
3. A solution of 0.100 M HCl and a solution of 0.100 M NaOH are prepared. A 40.0 mL sample of one of
the solutions is added to a beaker and then titrated with the other solution. A pH electrode is used
to obtain the data that are plotted in the titration curve shown below.
a.
b.
c.
d.
Identify the solution that was initially added to the beaker. Explain your reasoning.
On the titration curve above, circle the point that corresponds to the equivalence point.
At the equivalence point, how many moles of titrant have been added?
The same titration is to be performed again, this time using an indicator. Use the information in
the table below to select the best indicator for the titration. Explain your choice.
Indicator
pH Range of Color Change
Methyl violet
0 – 1.6
Methyl red
4–6
Alizarin yellow
10 – 12
e. What is the difference between the equivalence point of a titration and the end point of a
titration?
f. On the grid provided on the next page, sketch the titration curve that would result if the
solutions in the beaker and burette were reversed (i.e., if 40.0 mL of the solution used in the
burette in the previous titration were titrated with the solution that was in the beaker).
4. Methane gas reacts with chlorine gas to form dichloromethane and hydrogen chloride, as
represented by the equation below.
CH4(g) + 2 Cl2(g) → CH2Cl2(g) + 2 HCl(g)
a. A 25.0 g sample of methane gas is placed in a reaction vessel containing 2.58 mol of Cl2 (g).
i. Identify the limiting reactant when the methane and chlorine gases are combined. Justify
your answer with a calculation.
ii. Calculate the total number of moles of CH2Cl2(g) in the container after the limiting reactant
has been totally consumed.
The following mechanism has been proposed for the reaction of methane gas with chlorine gas.
All species are in the gas phase.
Step 1
Clଶ ⇄ 2 Cl
fast equilibrium
Step 2
CHସ + Cl → CHସ + HCl
slow
fast
Step 3
CHଷ + Clଶ → CHଷ Cl + Cl
fast
Step 4
CHଷ Cl + Cl → CHଶ Clଶ + H
Step 5
H + Cl → HCl
fast
b. In the mechanism, is CH3Cl a catalyst, or is it an intermediate? Justify your answer.
c. Identify the order of the reaction with respect to each of the following according to the
mechanism. In each case, justify your answer.
i. CH4(g)
ii. Cl2(g)
5. The structures for glucose, C଺ Hଵଶ O଺, and cyclohexane, C଺ Hଵଶ , are shown below.
a. Identify the type(s) of intermolecular forces in
i. Pure glucose
ii. Pure cyclohexane
b. Glucose is soluble in water but cyclohexane is not soluble in water. Explain.
c. Consider the two processes represented below.
Process 1: Hଶ O ሺlሻ → Hଶ O(g)
Δ‫ ܪ‬଴ = +44.0 kJ/mol
ଵ
Process 2: Hଶ O ሺlሻ → Hଶ ሺgሻ + ଶ Oଶ (g) Δ‫ ܪ‬଴ = +286 kJ/mol
i. For each of the two processes, identify the type(s) of intermolecular or intramolecular
attractive forces that must be overcome for the process to occur.
ii. Indicate whether you agree or disagree with the statement “When water boils, H2O
molecules break apart to form hydrogen molecules and water molecules.” Support your
answer with a short explanation.
6. The following redox reaction occurs in an acidic solution:
ଷା
ଶା
Feଶା ሺaqሻ + MnOି
ସ ሺaqሻ → Fe (aq) + Mn (aq)
a. Write the balanced reaction.
b. What is the oxidation number of manganese in the permanganate ion, MnOି
ସ (aq)?
c. Identify the reducing agent in the reaction represented above.
7. A student is assigned the task of determining the number of moles of water in one mole of MgCl2 ⋅ n
H2O. The student collects the data shown in the following table.
Mass of empty container
22.347 g
Initial mass of sample and container
25.825 g
Mass of sample and container after first heating
23.982 g
Mass of sample and container after second heating
23.976 g
Mass of sample and container after third heating
23.977
a. Explain why the student can correctly conclude that the hydrate was heated a sufficient number
of times in the experiment.
b. Use the data above to
i. calculate the total number of moles of water lost when the sample was heated, and
ii. determine the formula of the hydrated compound.
c. A different student heats the hydrate in an uncovered crucible, and some of the solid spatters
out of the crucible. This spattering will have what effect on the calculated mass of the water lost
by the hydrate? Justify your answer.
8. Two clear, colorless solutions are mixed. A 125 mL of solution made with 0.150 g sample of solid
lead(II) nitrate is added to 125 mL of 0.100 M sodium iodide solution. The chemical reaction that
takes place is represented by the following equation.
Pb(NO3)2(aq) + 2 NaI(aq) → PbI2(s) + 2 NaNO3(aq)
a. List an appropriate observation that provides evidence of a chemical reaction between the two
compounds.
b. Calculate the number of moles of each reactant.
c. Identify the limiting reactant. Show calculations to support your identification.
d. Calculate the molar concentration of NOି
ଷ (aq) in the mixture after the reaction is complete.
e. Circle the diagram below that best represents the results after the mixture reacts as completely
as possible. Explain the reasoning used in making your choice.
9. Hydrofluoric acid, HF(aq), dissociates in water as represented by the equation below.
HF ሺaqሻ ⇄ H ା ሺaqሻ + F ି (aq)
Ka =7.3 x 10–4
a. Write the equilibrium-constant expression for the dissociation of HF in water.
b. Calculate the molar concentration of H+ in a 0.40 M HF(aq) solution.
HF (aq) reacts with NaOH (aq) according to the reaction:
HF ሺaqሻ + OH ି ሺaqሻ → Hଶ Oሺlሻ + F ି (aq)
A volume of 15 mL of 0.40 M NaOH (aq) is added to 25 mL of 0.40 M HF (aq) solution. Assume the
volumes are additive.
c. Calculate the number of moles of HF (aq) remaining in the solution.
d. Calculate the molar concentration of F– (aq) in the solution.
e. Calculate the pH of the solution.
10. Answer the following questions about electrochemical cells.
It is observed that when silver metal is placed in aqueous thallium (I) fluoride, TlF, no reaction
occurs. The standard reduction potential for Ag+ + e– → Ag is 0.80 V. When the switch is closed in the
cell represented above, the voltage reading is +1.14 V.
a. Write the reduction half-reaction that occurs in the cell.
b. Write the equation for the overall reaction that occurs in the cell.
c. Identify the anode in the cell. Justify your answer.
d. On the diagram above, use an arrow to clearly indicate the direction of electron flow as the cell
operates.
e. Calculate the value of the standard reduction potential for the Tl+/Tl half-reaction.
The standard reduction potential, E0, of the reaction Pt2+ + 2 e– → Pt is 1.20 V.
f. Assume that electrodes of pure Pt, Ag, and Tl are available as well as 1.00 M solutions of their
salts. Three different electrochemical cells can be constructed using these materials. Identify the
two metals that when used to make an electrochemical cell would produce the cell with the
largest voltage. Explain how you arrived at your answer.
g. Predict whether Pt metal will react when it is placed in 1.00 M AgNO3(aq). Justify your answer.
11. Answer the following questions that relate to laboratory observations and procedures.
a. An unknown gas is one of three possible gasses: carbon dioxide, hydrogen, or oxygen. For each
of the three possibilities, describe the result expected when the gas is tested using a glowing
splint (a wooden stick with one end that has been ignited and extinguished, but still contains
hot, glowing, partially burned wood).
b. The following three mixtures have been prepared: CaO plus water, SiO2 plus water, and CO2 plus
water. For each mixture, predict whether the pH is less than 7, equal to 7, or greater than 7.
Justify your answer.
12. Consider the four reaction-energy profile diagrams shown below.
a. Identify the two diagrams that could represent a catalyzed and an uncatalyzed reaction pathway
for the same reaction. Indicate which of the two diagrams represents the catalyzed reaction
pathway for the reaction.
b. Indicate whether you agree or disagree with the statement, “Adding a catalyst to a reaction
mixture adds energy that causes the reaction to proceed more quickly.” Support your answer
with a short explanation.
13. Ununoctium-294 was created by fusing californium-249 and calcium-48.
a. Write the balanced reaction for the fusion.
b. How many neutrons are ejected from the nucleus during the fusion process?
c. Uuo-294 undergoes three alpha decays shortly after formation. What is the final result of the
three decays?
14. Answer the following questions about a pure compound that contains only carbon, hydrogen, and
oxygen.
a. A 0.7549-g sample of the compound burns in O2 (g) to produce 1.9061 g of CO2 (g) and 0.3370 g
of H2O (g).
i. Calculate the individual masses of C, H, and O in the 0.7549-g sample.
ii. Determine the empirical formula for the compound.
b. A 0.5246-g sample of the compound was discovered in 10.0012 g of lauric acid, and it was
determined that the freezing point of lauric acid was lowered by 1.68°C. The value of ‫ܭ‬௙ of lauric
acid is 3.90°C/m. Assume that the compound does not dissociate in lauric acid.
i. Calculate the molality of the compound dissolved in lauric acid.
ii. Calculate the molar mass of the compound from the information provided.
c. Calculate the molecular formula of the compound based on your answers above.
d. Further tests indicate that a 0.10 M aqueous solution of the compound has a pH of 2.6.
i. Identify the organic functional group that accounts for this pH.
ii. Determine the ‫ܭ‬௔ for the compound.
15. A pure sample of lanthanum (III) carbide (LaC2(s)), of unknown mass, is reacted with excess H2O (l)
via the following reaction:
2 LaCଶ ሺsሻ + 6 Hଶ O ሺlሻ → Cସ H଺ ሺgሻ + 2 LaሺOHሻଷ (s)
Suppose that the only gaseous produce is 1,3-butadiene, C4H6 and that it is collected over water at
23.0°C. The barometric pressure is 743.0 mm Hg and the volume of the collected gas is 47.1 mL. At
23°C, the vapor pressure of water is 21.1mm Hg
a. Determine the moles of C4H6 (g) collected.
b. Determine the mass of LaC2 (s) originally reacted.
16. Represented below are five identical balloons, each filled to the same volume at 25°C and 1.0
atmosphere pressure with the pure gas indicated.
a. Which balloon contains the greatest mass of gas? Explain.
b. Compare the average kinetic energies of the gas molecules in the balloons. Explain.
c. Which balloon contains the gas that would be expected to deviate most from the behavior of an
ideal gas? Explain.
d. Twelve hours after being filled, all the balloons have decreased in size. Predict which balloon will
be the smallest. Explain your reasoning.